Resistance unit



Oct. 14, 1958 G. E. FISHER 2,856,496-

RESISTANCE UNIT Filed March 8, 1956 2 Sheets-Sheet 1 Oct. 14, 1958 G, Ef FISHER 2,856,496

RESISTANCE UNIT Filed March 8, 1956 2 Sheets-Sheet 2 NVENTOR BY 5. 7w 4/ Al/N EYS UnitedStates Patent RESISTANCE UNIT George E. Fisher, Ambler, Pa., assignor to Trent, Inc., Philadelphia, Pa., a corporation of Delaware Application March 8, 1956, Serial No. 570,382

4 Claims. (Cl. 201-69) This invention relates to high-temperature electrical resistance or heating units and, in particular, relates to improvements in the type of unit disclosed in Patent No. 1,928,142.

The resistance unit shown in the above-mentioned patent is made up of strip or ribbon-like metal formed into a continuous sinuousgrid having a plurality of elongated sections or legs arranged parallel to one another, adjacent legs being interconnected by crossover sections, the principal use of such a unit being for industrial furnaces and the like.

The principal object of the invention is to provide a heating element or resistance unit which retains all the advantages of the unit of said patent but, in addition, provides other important advantages, for example, as set forth following.

One advantage of the invention is in the providing of a resistance unit of the character described wherein the leg and crossover sections are arranged to obtain increased utilization of available radiation surfaces.

Another advantage of the invention is in the providing of a resistance unit of the character described having improvements in the crossover and leg sections enabling operation at temperatures considerably higher than possible with a comparable unit as disclosed in said patent.

Another advantage of the invention is in the providing of a resistance unit of the character described wherein the temperature along the strip or ribbon forming the unit is substantially uniform.

Another advantage of the invention is in the providing of a resistance unit of the character described wherein the leg and crossover sections are arranged so that the crossover, and particularly the area interconnecting the two sections, does not become a hot spot.

Another advantage of the invention is in the providing of a resistance unit of the character described wherein the leg and crossover sections are arranged to permit approximately more resistance in a given area over that obtainable with a comparable unit as disclosed in said patent.

Another advantage of the invention is in the providing of a resistance unit of the character described wherein each leg section is axially angularly oriented, thereby obtaining increased utilization of available radiation surfaces.

Another advantage of the invention is in the providing of a resistance unit of the character described wherein the crossover section is V-shaped, thereby obtaining increased utilization of available radiation surfaces.

Another advantage of the invention is in the providing of a resistance unit of the character described wherein a crossover section is arranged to project away from the edges of the legs whereby to form a support for the purpose of spacing the unit away from a furnace bottom and preventing hot spots.

Another advantage of the invention is in the providing of a resistance unit of the character described wherein the legs are tilted and certain crossover sections project away from the edges of the legs, the crossover and the edges of the legs cooperating to form a support for spacing the unit away from a furnace bottom.

Another advantage of the invention is in the providing of a resistance unit of the character described wherein the crossover section is comprised of two planar portions each extending away from corresponding ends of the leg sections and angled to each other and joined to form the apex of a V, such arrangement providing for the increase of spacing between the crossover and legs and preventing hot spots.

The manner in which the foregoing objects and advantages are obtained together with other objects and advantages of the invention will be apparent from the following description and drawings wherein:

Figure 1 is a plan view of a heating or resistance unit constructed in accordance with the invention;

Figure 2 is a cross section taken on the line 2-2 of Figure 1;

Figure 3 is a side elevation of the unit looking forward the right in Figure 2;

Figure 4 is a cross section taken on the line 44 of Figure 2;

Figures 5 and 6 are diagrammatic views illustrating radiation and other advantages of the invention; and

Figure 7 is a diagrammatic plan view illustrating the sections of the heating element radially disposed.

Before proceeding with the detailed description, it is desired to point out that the material from which the units of the invention are made may be of any suitable resistance metal or alloy formed into a grid of desired shape and dimensions. Preferably the metal is in strip or ribbon-like form, with the cross section rectangular and of constant area throughout its length. As will appear below, the strip is folded and formed into the shape desired and this can be done either manually or by automatic machines.

In Figure 1 the grid 1 is generally rectangular in shape and is made up of elongated sections or legs 2-7 which are integrally connected as by crossover sections. The legs 23, 4-5 and 67 are connected by crossovers 8, 9 and 10, which overlie the plane of the legs, while the legs 3-4 and 5-6 are joined by crossovers 11 and 12, which underlie the plane of the legs. The end portions 14 and 15 on legs 2 and 7 are adapted to be connected to a source of electrical power so as to pass current through the unit and heat up the same. Each leg has planar portions 2a, etc., and also strengthening corrugations such as indicated at 2b, etc.

As seen in Figures 1 and 2, each of the legs 2--3, etc., is axially angularly oriented so that the pairs 2--3, 4-5 and 6--7 form channels V V and V As will be apparent from Figure 2, the channels are generally concave in the sense of being V or U-shaped, depending on whether the cross section of a channel is taken across the planar or across the corrugated portion of the legs. When the grid of Figure l is used in a furnace, the unit is arranged so that the channels face the interior space.

The orienting or tilting of the legs as above described has important advantages. For example, in Figure 5 there is diagrammatically shown the cross sections of legs of a typical resistance unit, for example, the legs 2', 3', 4, 5', etc., arranged adjacent afurnace wall or bottom 17. (In this illustration the arcuate lines represent the corrugations in the various legs while the straight lines represent the planar portions.) It will be apparent that the top surfaces of each of the legs are fully exposed to the accepting body, i. e., the interior of the furnace or the charge and, therefore, all the radiation from these sur-' faces will be utilized. Further, it will be apparent that the amount of radiating surface the accepting body can see is increased because. the legs are tilted at an acute which connect with the crossover.

angle and, therefore, the bottom surface is able to radiate into'the interior. For example, the interior of "the furnace can see the underside of the planar portion of the leg 3 through the angle a and also see the underside of the arcuateportion-through.the angle-,8. Similar effects pertainfor'the underside of'the other legs.

Increase of radiation, of course, meansincrease in the eificiency of bothf'the'unit and the furnace operation and in a given furnace to operate at. higher temperatures and/or to come up .to temperature in'a shorter time. All of the foregoing'have important industrial advantages.

The increased radiation as mentioned above, of course, is in marked contrast to'the situation with a unit. as disclosed in said patent where only thetop radiating surface is exposed to the body. to beheated. This will be readily apparent'from an inspection of Figure 5 where'the legs of the ordinary unit are indicated in dotted lines 18 and 1.9.

There is another advantage in tilting the legs, and this is in connection with the spacing of a unit from the'furnace bottom. This will be taken up in more. detail hereinafter.

Each of the crossovers is identical in construction and only crossover Swill be described in detail following.

It'Will be noted that the ends of the legs. 2 and 3 are angled .andhave oppositely upturned edges 20'and 21 (A similar arrangement pertains to the other legs andcrossovers.) The crossover 8 comprises atriangular-shaped.generally planar portion 22, one side of which is integral with the edge. 20 and agenerally planar'triangular-shaped portion 23,one edge of which is integral with the edge 21. The portions 22 and23-are angled or disposed at approximately 90 with respect to the surfaces of legs 2 and 3 and, therefore, project upwardly and are integrally joined at 24. It will be noted that the angle between the portions is substantially less than 180. As best seen in Figures 3 and 4,' the top portion 8a of the crossover 8 projects away from a plane through the outer longitudinal edges 25 and 26 of the legs 2 and 3. The configuration of the crossover is generally that of a V with the apex being located at 24.

The crossovers 9 and are identical with crossover 8 and the crossovers 11 .and 12 are similarly formed, the principal diflFerence being that these latter crossovers project away from the lower edgesof the legs. For example, the top portion 110: of crossover 11 projects away from a plane through the longitudinal edges 30 and 31 of legs .31and 4.

The. arrangement of the crossovers .asabove described has several distinct advantages.

"First, with respect to radiation, it will be observed that not only all of the top surfaces of the crossovers 8, 9 and 10 are exposed to the space to be heated but, in-addition, the space orangular disposition between the crossover and the legs makes the bottom surface of the crossover completely exposed to certain portions of the space to be heated..and partially exposed to the other portions. Thus, the availablesurfaces are more fully utilized forradiation purposes. In .connection with crossovers 11 and 12, it will be noted that the spacing between legs and crossovers makes certain portions of the-crossovers fully exposed .to the space to be heated.

When the. crossovers and legs. are-arranged in the. manner. described, the crossovers, .and. particularly the-.Portionsjoiningthe same to the legs, readily dissipate heat and, therefore, do not develophot spots and thus permit higher temperature operation. as compared with units disclosedin saidpatent. This is of. especial advantage becauseradiation-surfaces shouldbe maintained at as high atemperatureas possible inasmuchas radiation increases with..the fourth. power of the absolute temperature.

The development of hot spots in units of the character described is undesirable because thelikelihoodof deter-ioration is increased and life expectancy of the. unit short ened. Thus,-it is 'highlydesirable to maintain-uniform temperature throughout the :length of the strip forming the unit and the above-described arrangement of legs and crossovers "is'instrumental in obtaining that objective.

Another advantage of the arrangement of the legs and crossovers will be described in connection with Figure 6, which illustrates what takes place when a unit is disposed on a furnace bottom. Here are shown the leg 32 and appended crossovers 33..and 34 .of a resistance unit disposed on a furnace floor 35. It will be observed that since the crossover 34 extendsiaway from .the edge 36 of the leg 32, the leg is spaced away .from the floor, the only point of direct contact'being a line contact withthe lower longitudinal edge as generally indicated at 37. This spacing is important as it revents the-formation of hot spots and permits higher temperature operation.

The spacing between the'legs "and crossovers has certain manufacturing advantages. For example, as shown in Figure 7, the crossovers 40 and 41 eflectively operate as pivots and permit the portions 42, 43 and 44 of a resistance unit to be separated in the manner indicated. Thus, the resistance -unit iseasily formed in a-circularfashion.

Another advantage of the tilting of the legsand the angling of. the crossovers is that approximately more resistance-can be obtained for a given area as compared to comparable units of said patent. This is important he cause itmeans more potential wattage or heat for a given size'unit.

Iclairn:

1. In a resistance unit, a pair of spaced ribbon-like sections disposed substantially parallel and axially angularly oriented with respect to each. other whereby to form aconcave channel; and a crossover portion extending acrosssaid channel." and connecting oppositely directed edges of said sections, the crossover portion being free from contact with said sections except at said edge portions said sections and said portion being integral and formed, from'strip metal and having the same cross sectionalarea.

2..In a resistance unit, a pair of spaced ribbon-like sections disposed substantially parallel and axially angularly oriented with respect to each other whereby to form a concave channel; and a crossover portio-n extending across said channel and connecting oppositely directed edges of said sections, the crossover portion being free from contact with said sections except at said edge portions and having aV-shaped portion projecting away from a plane containing corresponding longitudinal edges of saidsections said sections andsaid portion being integral and formed fromhstrip metaland having the same. cross sectionalarea...

3. In a resistance unit, a pair .of legs; a crossover connecting the legs and comprising two generally planar V-shaped portions respectively integrally connected with corresponding edges of said legs and integrally joined together at an angle substantially less than said legs and .said crossover beingformed from strip metal and having .the same cross sectional area.

4. In a resistance unit, a pair of spaced ribbon-like sections .disposed substantially parallel and axially angularly oriented with respect to eachother whereby to form a concave channel; and a crossover portion extending across said rchanneland connecting oppositely directed edges of said sections, the crossover portion being free from contact with said sections except at. said edge portions and having a V-shaped portion projecting away from-a plane containing corresponding longitudinal edges of said sections, said sections and said portion being integral and formed from strip metal and having the same cross sectional area and each said section being formed with an axially extendingcorrugation concave with respect to the channel.

.Trentet-al.. Sept. 26,-.1933 .Du-Boisv Jan. 5, 1954 

